Electric safety-box

ABSTRACT

Safety-box connected to pushbuttons comprising a first line and a second line, a control relay and a safety relay on each line, each relay jointly controlling a main contact and an auxiliary contact, the main contact of the control relay being normally open and the main contact of the safety relay being normally closed in the position of rest of the pushbuttons, the auxiliary contact of the control relay of the first line being connected in parallel with the rest contact of the pushbutton of a second line between a point located downstream of the main relay of the second line and the control winding of the safety relay of the said second line.

United States Patent [54] ELECTRIC SAFETY-BOX 8 Claims, 4 Drawing Figs.

[52] U.S.Cl 317/135, 317/9,317/l36 [51] lnt.-Cl ....H0lh47/l6 [50] FieldotSeai-ch 317/136, 135

[56] References Cited UNITED STATES PATENTS 2,786,989 3/1957 Smith 340/213 Primary Examiner-J. D. Miller Assistant Examiner-Harry E. Moose, Jr. Attorney- Karl W. Flocks ABSTRACT: Safety-box connected to pushbuttons comprising a first line and a second line, a control relay and a safety relay on each line, each relay jointly controlling a main contact and an auxiliary contact, the main contact of the control relay being normally open and the main contact of the safety relay being normally closed in the position of rest of the pushbuttons, the auxiliary contact of the control relay of the first line being connected in parallel with the rest contact of the pushbutton of a second line between a point located downstream of the main relay of the second line and the control winding of the safety relay of the said second line.

Patented May 18, 1971 I 2 Sheets- Sheet 1 Patented 'Ma 1s,1971 I 3,579,048

2 Sheets-Sheet 2 ELECTRIC SAFETY-BOX The present invention relates to a safety box giving an indication of a fault on an electric circuit, and more particularly for the prevention of accidents in an aircraft piloting control circuit as a result of the accidental sticking of relay contacts or of the fortuitous blocking of the control knobs in the closed position,

In systems having two electric circuits, such as those intended to reverse the direction of running of a motor or of any kind of electromechanical device, the fault which is most frequently encountered is that due to the accidental sticking of the contacts as a result of breaking the circtiit on an inductance and/or to the mechanical blocking of the control switches of the relays.

Although it is quite common practice to utilize in a circuit of this kind a so-called crossed relays system which, in the case of a sticking fault of the kind referred to, permits the systematic opening of a second contact on the circuit which it is not desired to energize, by means of the opposite-control switch, it still remains that the fault reappears as soon as the said opposite-control member is brought back into its initial position, while furthermore the fault is only detected at that moment when a bad operation of the mechanisms controlled is observed, which may be a very serious matter incertain cases.

A concrete case of the bad operation of a system of this kind is encountered in the aeronautical field.

The piloting of aircraft at high speed is in fact most frequently carried out by means of an auxiliary device for operating the elevator system, the control of which utilizes the principle of the system with crossed relays. As in fact this system has the major drawback of the risk of a fault in the relays by sticking of the contracts resulting from breaking or opening a circuit carrying a fairly large current on a inductive circuit, the pilot becomes aware too late that although he has released the dive or "climb" pushbutton, the aircraft continues its evolution following the order which was previously given.

An analysis of the operation of the system with crossed relays further reveals several other drawbacks resulting from the fact that the fault is not indicated to the pilot who is only warned by the undesired changes in the trim of the aircraft, which is particularly dangerous if the fault occurs, for example, when approaching to land, apart from the fact that the four relays of the crossed system operate continuously, which increases the risk of faults since the auxiliary safety relays are also subject to these faults, and finally without forgetting that when the fault has been neutralized by actuating the safety circuit breaker, it is no longer possible to utilize the mobile elevator aileron until the aircraft has landed.

In consequence, the invention provides a safety-box with crossed circuits, in which each relay actuating the main contacts on the lines comprises an auxiliary contact which forms part of the assembly of an auxiliary circuit, the said auxiliary contact of a circuit and the rest contact of the control button of the other circuit being connected in parallel between the winding of the safety relay of the said second circuit and a point on the line located downstream of the main contact of the said second circuit.

The electric safety-box according to the invention is further provided with an indicator pilot lamp on each auxiliary relay, in order to indicate its operation and in consequence the existence of a fault.

Other characteristic features and advantages of the invention will be brought out in the description which follows below with reference to the accompanying drawings and referring purely by way of indication but not in any limitative sense, to one form of embodiment of the invention.

In these drawings:

FIG. I is an electrical diagram of the conventional system of crossed relays;

FIG. 2 is an electrical diagram of the box with an auxiliary relay in accordance with the invention;

FIG. 3 is an electrical diagram showing the box according to the invention in a particular application for direct current to the control of the horizontal plane of an aircraft; and

FIG. 4 is a diagrammatic view in perspective, showing the arrangement of the various parts in an elevator control system comprising the boxes of FIG. 3.

In a conventional manner, when it is desired to protect two electric circuits against the risk of sticking of the contacts of the relays during the inductive breaking of a high current, there is employed, as shown in FIG. 1, a system with crossed relays. In this diagram, it can be seen that the high and low circuits l and 2 each pass through two relays, of which the one which is open is the corresponding control relay 3 or 4, and the other normally closed relay is the corresponding safety relay 5 or 6. Each top pushbutton 7 and bottom pushbutton 8 operates the coil of each corresponding control relay from a circuit in shunt to the main circuit and passing through the rest contact of the opposite pushbutton.

The normal operation of each circuit is then as follows:

Operation of the pushbutton 7, for example, causes the action of the control relay 3 which closes the circuit 1 and opens the other circuit 2 by means of the safety relay 6. Conversely, the button 8 actuates the control relay 4 which closes the circuit 2 and opens the circuit 1 by means of the safety relay 5.

It can be seen that in this way, a safety relay always opens on a circuit when the control relay of the opposite circuit is closed, which thus avoids the risk of double supply to the controlled member, at the same time producing the required safety measure of opening the defective circuit from the opposite pushbutton.

However, as has already been emphasized, the circuits remain in a condition of instability, since the putting to rest of the pushbuttons leaves a relay closed when the latter has its contact accidentally stuck, the only recourse in such a case being in fact to act in counter-reaction on the opposite pushbutton in order to open the control relay. In addition, no indication of the fault is given, and no recourse is then possible apart from the interruption of the circuits, if the second control relay becomes subject to a fault of the same kind.

In the electric box according to the invention, the essential principle of the crossed-relay system is retained, but in addition, each control circuit is duplicated by an auxiliary safety circuit.

In the electrical diagram of this box which is shown in FIG. 2, each control relay is provided with an auxiliary contract, one terminal of which takes the current of the opposite line downstream of the main control relay (the arrow f, indicates the direction of the direct current).

During a mechanical blocking of one of the pushbuttons in the operating position, the corresponding circuit is interrupted when the other pushbutton is actuated, by means of this auxiliary contact which opens defective circuit by the safety relay which it controls.

All cases of operation of safety relays which always correspond to a defect either of a control relay or of a pushbutton, are indicated by means of a pilot indicator lamp supplied from an auxiliary contact provided on each of these safety relays.

In the particular case which corresponds to the control of the elevator system of an aircraft and which is shown diagrammatically in FIG. 4, the control column 11 is equipped with two pushbuttons l2 and 13 and the electric safety-box 14 according to the invention controls the elevator surface 16 through the intennediary of a motor 17, while two limit switches 18 and 19 limit the extreme positions of the control surface and the circuit is protected by a circuit breaker 25.

An installation of this kind thus comprises the electric safety-box according to the invention, and is further provided with an auxiliary box 15 which essentially houses the diode equipment and other circuit elements appropriate to a directcurrent circuit such as that installed on aircraft.

The box 14 which is shown in more details in FIG. 2, comprises essentially the two control relays 20 and 21 and the two Nature of fault safety relays 22 and 23. The auxiliary box which is shown in greater details in FIG. 3, comprises in the installation considered, four diodes 34, 35, 36 and 37 intended to prevent voltage surges during the breaking of the relays, two test indicators 32 and 33 and two diodes 38 and 39 for locking the main circuits, with their protection diodes and 41.

Finally, an emergency switch 24 is provided on the box 15 so as to enable manual isolation of the two circuits by opening the safety relays 22 and 23.

Table 1 given below summarizes the cases of faults and the operations which result from the action to be carried out in such cases. The direct current circulates inthe lines in the direction of the arrow f,.

TABLE 1 Action to be taken and operations which result Button 13 is released, position R, opens 22 by the circuit 50, 22, 61, 13, 52 taken off at 52 down stream of 20. The indicator 33 lights-up.

Button 12 is released, position R opens 23 by the circuit 60, 23, 61, 12, 62 taken off at 62 downstream of 21 in the position of closure. The indicator 33 lights-up.

When the button 12 is depressed, it closes 21 which opens 22 by its auxiliary contact 63 having taken the current at 52 downstream of 20 in the position of closure. The indicator 32 lights-up.

When the button 13 is depressed, it closes 20 which opens 28 by its auxiliary contact 64 having taken the current at 62 downstream of 21 in the closed position. The indicator 33 lights-up.

Relay 20 locked in the closed position.

Relay 21 locked in the closedposition.

Button 13 locked in the closed position (Position M).

Button 12 locked in the closed position (Position M).

Relays 20 and 21 locked in the The two circuits are opened by closed position.

supplying the relays 22 through the circuit 50, 22, 51, 63, 52 and 23 through the circuit 60, 23, 61, 64, 62, the auxiliary contacts 63 and 64 of the relays 20 and 21 being closed. The indicators 22 and 23 light-up.

The two indicators 32 and 33 light-up.

Due to their closure, 20 and 21 open the two relays 22 and 23. The indicators 22 and 23 light-up.

21 is closed and 22 is opened as a result of the closure of 12,'and 23 is opened by the closure of 20. The two circuits are open and the two indicators 32 and 33 are lighted-up.

Buttons 12 and 13 locked in the closed position (Position M).

Buttons 12 and 13 locked in the closed position (Position M) and 20 and 21 locked while closed.

Button 13 locked in the closed position (position A) and 21 locked when closed.

Button 12 locked in the closed position (position A) and 20 is locked when closed.

it is therefore clear that in emergency the switch 24 brings the current supplied by the lines 1 and 2 to the relays 22 and 23. The electric box according to the invention provides a safety measure against all the defects of the relays or of the pushbuttons by means of a simple auxiliary circuit, and the fault is indicated by a light indicator. In addition, the control relays only operate in the event of a fault, which increases their reliability. The box can easily be changed by virtue of the arrangement of the output terminals which may be plug-in connections.

It will of course be understood that the present invention position and a safety contact in the position of rest, a first line' and a second line, both connected to a current source, a control relay and a safety relay series connected in each line, each relay simultaneously controlling a main contact and an auxiliary gauged contact, said main contact on said lines of said control relay being normally open and said main contact of said safety relays on said lines being nonnally closed in the position of rest of said pushbuttons, said auxiliary contact of said control relay of said first line being connected in parallel with said safety contact of said pushbutton in said second line between a point located downstream of said control relay of said second line and the control winding of said safety relay of said second line.

2. A safety-box as claimed in claim 1, characterized in that the auxiliary contact of the safety relay of the first line establishes, when it is closed, a short circuit line between the current source and a first pilot lamp which lights-up.

3. A safety-box as claimed in claim 1, characterized in that the auxiliary contact of the safety-relay of the second line establishes, when it is closed, a short circuit line between the current source and a second indicator pilot lamp which lights up.

4. A safety-box as claimed in claim 1, characterized in that all the auxiliary contacts are normally open when the pushbuttons are in the position of rest.

5. A safety-box as claimed in claim 1, characterized in that, relay, the pushbutton of the first line is in the operating position, the control relay of the corresponding line is closed, the safety relay of the second line being then excited by means of the auxiliary contact of the said relay, when the second line is supplied downstream of the main contact of the-control relay of said second line.

6. A safety-box as claimed in claim 5, characterized in that the pushbutton of a first line being actuated to the operating position and the main contact of the control relay of a second line being accidentally stuck in the closed position, the safety relay of said second line is excited by the circuit which passes through the auxiliary contact of the control relay of said first put into the working position, the safety relay of said first line is excited by the closure of the auxiliary contract of the control relay of said second line which closes, the operation of said safety relay opening the corresponding main contact which interrupts the current in the first line and closes the auxiliary contact of said relay, thereby causing a pilot lamp to light and indicate the fault.

8. A safety-box as claimed in claim 1, characterized in that the main contact of a control relay of a first line being stuck and the corresponding pushbutton returning to its position of rest, the corresponding safety relay is excited by a circuit passing through the safety contact in the position of rest of said pushbutton, and being supplied with current downstream of said stuck main contact. 

1. A safety-box on a current source comprising two pushbuttons having a momentary action at will with automatic return to the position of rest contact when the order is terminated, establishing an operating contact in the working position and a safety contact in the position of rest, a first line and a second line, both connected to a current source, a control relay and a safety relay series connected in each line, each relay simultaneously controlling a main contact and an auxiliary gauged contact, said main contact on said lines of said control relay being normally open and said main contact of said safety relays on said lines being normally closed in the position of rest of said pushbuttons, said auxiliary contact of said control relay of said first line being connected in parallel with said safety contact of said pushbutton in said second line between a point located downstream of said control relay of said second line and the control winding of said safety relay of said second line.
 2. A saFety-box as claimed in claim 1, characterized in that the auxiliary contact of the safety relay of the first line establishes, when it is closed, a short circuit line between the current source and a first pilot lamp which lights-up.
 3. A safety-box as claimed in claim 1, characterized in that the auxiliary contact of the safety-relay of the second line establishes, when it is closed, a short circuit line between the current source and a second indicator pilot lamp which lights up.
 4. A safety-box as claimed in claim 1, characterized in that all the auxiliary contacts are normally open when the pushbuttons are in the position of rest.
 5. A safety-box as claimed in claim 1, characterized in that, relay, the pushbutton of the first line is in the operating position, the control relay of the corresponding line is closed, the safety relay of the second line being then excited by means of the auxiliary contact of the said relay, when the second line is supplied downstream of the main contact of the control relay of said second line.
 6. A safety-box as claimed in claim 5, characterized in that the pushbutton of a first line being actuated to the operating position and the main contact of the control relay of a second line being accidentally stuck in the closed position, the safety relay of said second line is excited by the circuit which passes through the auxiliary contact of the control relay of said first line and receiving current downstream of said main contact, a pilot lamp corresponding to this operational fault being lighted by means of a circuit passing through an auxiliary contact of said safety relay.
 7. A safety-box as claimed in claim 1, characterized in that, when the pushbutton of said first line is stuck in the working position, the main contact of the control relay of said first line remaining closed and the pushbutton of said second line being put into the working position, the safety relay of said first line is excited by the closure of the auxiliary contract of the control relay of said second line which closes, the operation of said safety relay opening the corresponding main contact which interrupts the current in the first line and closes the auxiliary contact of said relay, thereby causing a pilot lamp to light and indicate the fault.
 8. A safety-box as claimed in claim 1, characterized in that the main contact of a control relay of a first line being stuck and the corresponding pushbutton returning to its position of rest, the corresponding safety relay is excited by a circuit passing through the safety contact in the position of rest of said pushbutton, and being supplied with current downstream of said stuck main contact. 